1. Field of the Invention
The invention relates to a proportional solenoid valve for a camshaft adjusting device of motor vehicles. The proportional solenoid valve comprises a valve housing in which a piston is slidably arranged and which comprises at least one working connector, a tank connector, and a pressure connector. Via the pressure connector, a pressure medium, preferably hydraulic oil, can be supplied to the piston. The piston is provided with at least one passage for the pressure medium.
2. Description of the Related Art
Camshaft adjusting devices are used for adjusting the fuel consumption of an internal combustion engine in accordance to the momentary power demand. In this connection, the stroke of the intake valves is adjusted such that the fuel quantity required for the momentary power demand is injected into the combustion chamber. In order to change the valve stroke, the camshaft is rotated relative to the crankshaft. For this purpose, an adjuster is provided that can be compared to a hydro cylinder. The hydraulic oil of the internal combustion engine is used as the pressure medium. The pressure oil source is the lubricant circuit of the internal combustion engine. The actuation of the adjuster is realized by means of the proportional solenoid valve.
Essentially two types of adjusters are used, i.e., helical gear adjusters and blade type adjusters. The pressure medium is supplied by the proportional solenoid valve by means of a rotary translator to the adjuster. The rotary translator exhibits leakage to a greater or lesser extent. It is a problem in this connection that the leakage volume between the two working connectors differs.
The helical gear adjusters have greater internal friction than the blade type adjusters. On the other hand, a certain friction is better for vibration damping. The proportional solenoid valves of the known camshaft adjusting devices must ensure a hydraulic clamping of the adjusting element. In the case of helical gear adjusters, the adjusting element is a piston while in the case of blade type adjusters a rotor with radially projecting blades is used as the adjusting element. In the case of helical gear adjusters it is sufficient to provide a run-off control for hydraulic clamping of the piston. The blade type adjusters, in combination with the rotary translators, exhibit relatively great leakage; this has the result that the adjusting element cannot be optimally clamped. An additional problem is that, when insufficient oil pressure is present in one of the pressure chambers of the adjuster, the locking mechanism is no longer released.